carbon dioxide

American  

[kahr-buhn dahy-ok-sahyd] / ˈkɑr bən daɪˈɒk saɪd /

noun

1. a colorless, odorless, incombustible gas, CO 2 , present in the atmosphere and formed during respiration, usually obtained from coal, coke, or natural gas by combustion, from carbohydrates by fermentation, by reaction of acid with limestone or other carbonates, or naturally from springs: used extensively in industry as dry ice, or carbon dioxide snow, in carbonated beverages, fire extinguishers, etc.

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carbon dioxide British  

noun

1. Also called: carbonic-acid gas.  a colourless odourless incombustible gas present in the atmosphere and formed during respiration, the decomposition and combustion of organic compounds, and in the reaction of acids with carbonates: used in carbonated drinks, fire extinguishers, and as dry ice for refrigeration. Formula: CO 2

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carbon dioxide Scientific  

1. A colorless, odorless gas that is present in the atmosphere and is formed when any fuel containing carbon is burned. It is breathed out of an animal's lungs during respiration, is produced by the decay of organic matter, and is used by plants in photosynthesis. Carbon dioxide is also used in refrigeration, fire extinguishers, and carbonated drinks. Chemical formula: CO ₂ .

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carbon dioxide Cultural  

1. A compound made up of molecules containing one carbon atom and two oxygen atoms.

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Discover More

Carbon dioxide is normally found as a gas that is breathed out by animals and absorbed by green plants. The plants, in turn, return oxygen to the atmosphere. (See carbon cycle and respiration.)

Carbon dioxide is also given off in the burning of fossil fuels (see greenhouse effect).

Etymology

Origin of carbon dioxide

First recorded in 1870–75

Compare meaning

How does carbon-dioxide compare to similar and commonly confused words? Explore the most common comparisons:

• carbon monoxide vs. carbon dioxide

Example Sentences

As for carbon dioxide emissions, it would be the equivalent, annually, of taking 400,000 cars off the road, the commission said.

From Los Angeles Times • Jun. 13, 2026

Soda syrup and carbonated water were kept just above freezing to trap more carbon dioxide and increase the fizz.

From The Wall Street Journal • Jun. 13, 2026

The recovered carbon dioxide can then be stored or converted into other products, keeping it out of the atmosphere over the long term.

From Science Daily • Jun. 11, 2026

Perhaps the best-known examples of fermentation are in baking and brewing, where yeast breaks down sugar into ethanol and carbon dioxide.

From BBC • Jun. 4, 2026

“Well, not technically allergic, but they give me digestive issues that, um...You know like when tiny amounts of hydrogen, carbon dioxide, and methane combine with hydrogen sulfide and ammonia in the large intestine?”

From "Sir Fig Newton and the Science of Persistence" by Sonja Thomas